Directional couplers may be used to monitor signal quality/strength and/or for splitting off a low percentage of the signal present in a transmission line such as a coaxial cable. A dual directional coupler may be used to detect simultaneous forward and reflected power levels, for example, to monitor the Voltage Standing Wave Ratio (VSWR) of a communication system.
Prior dual directional couplers, for example as shown in FIGS. 19 and 20, typically comprise a body comprised of two halves that mate together with a cylindrical bore formed between the two halves. The bore sidewall surfaces form an outer conductor and an inner conductor is supported coaxially within the bore. Connection interfaces at each end of the bore allow the directional coupler to be inserted in-line with a coaxial cable and/or the coaxial connection interfaces of other RF components or equipment. During manufacture, the two halves body configuration requires multiple separate workpiece setup and machining operations, including precision machining of the planar mating surfaces of each half, grinding of bore and coupler grooves and then assembly of the halves together prior to cutting of threads at the bore and coupler ports. Also, the mating seam between the two halves creates an opportunity for eventual failure of the selected environmental seal solution.
The alignment precision of coupling elements arranged coaxially within coupling slots open to the bore is a significant factor of directional coupler electrical performance. Uniformly isolated from the body and supported only at the coupler ports at the periphery of the body, the coupling elements must be dimensioned with enough rigidity to withstand expected vibration and impact shock levels. The coupler elements are typically brazed or soldered together from multiple portions, a manufacturing operation requiring a skilled operator. Manufacture and installation of the coupler elements to specification represents a significant quality control issue during coupler manufacture. Tolerance variances occurring across each of the multiple elements of the body and coupler accumulate, often requiring time-consuming tuning of individual units to meet design specifications.
Therefore, it is an object of the invention to provide an apparatus that overcomes deficiencies in the prior art.